A hydraulic excavator as a typical example of the construction machine is generally constituted by an automotive lower traveling structure, an upper revolving structure rotatably mounted on the lower traveling structure, and a working mechanism tiltably provided on a front part of the upper revolving structure.
The upper revolving structure includes a revolving frame forming a support structural member, an engine mounted on a rear side of the revolving frame, and a cab provided on a front left side of the revolving frame which is a left side of the working mechanism. An operator's seat on which an operator is seated and the like are provided in the cab.
A connecting pin for mounting the working mechanism is provided on front sides of left and right vertical plates constituting the revolving frame. An oil reservoir tank such as a hydraulic oil tank storing hydraulic oil is provided on an outer side of the revolving frame in a left-right direction on a side opposite to the cab by sandwiching the working mechanism, a fuel tank storing fuel. This oil reservoir tank is arranged so that its front end is located on a rear side from the connecting pin of the revolving frame.
On the other hand, a diesel engine is used for an engine of the hydraulic excavator. This diesel engine emits a large amount of nitrogen oxides (hereinafter referred to as NOx). Thus, as a post-processing device of an exhaust gas of the diesel engine, there is a NOx purifying device for purifying NOx. This NOx purifying device is constituted by a urea selective reduction catalyst provided in an exhaust pipe of the engine and removing NOx in the exhaust gas, a reducing agent tank storing a urea water solution as the reducing agent, a urea injection valve injecting the urea water solution in the reducing agent tank to an upstream side of the urea selective reduction catalyst, and a connecting pipeline for connecting the reducing agent tank and the urea injection valve, for example.
Here, when the reducing agent tank is to be provided in the hydraulic excavator, it is desirable that a capacity is set large in order to reduce the number of times of supplying the reducing agent. However, since many devices are mounted on the hydraulic excavator, it is difficult to ensure a space where a large reducing agent tank is newly installed. Thus, a hydraulic excavator constituted such that two accommodating cases are arranged by being stacked vertically on a front side of the oil reservoir tank, and a reducing agent tank is accommodated in a lower accommodating case having a large capacity, while an article is accommodated in an upper accommodating case is disclosed (see, Patent Document 1, for example).